Fuel Pressure - Not rising?

[NTICEN]

Hi Guys,

Just wondering if anyone would have any ideas... Been having a few issue\'s with my fuel pressure not rising over the base idle set while driving?

After talking to a few people there suggestions were Fuel pump, regulator and injectors

so i brought a brand new walbro and installed it - no difference

hard wired the fuel pump - no difference

Brand new tomei regulator (not a knock off like my last one...) no difference

second hand factory grey injectors out of my mates wrx which was going fine - no difference

the way i have been testing my fuel pressure was to have another external gauge mounted up on the windscreen to confirm

Also to make sure the regulator was seeing boost pressure i hooked up another inline boost gauge which showed it was seeing boost

The regulator vacuum line does not have anything else being teed off it

Fuel pressure sits at 43psi @ idle with vacuum line disconnected - if i adjust it up to 50-60psi it holds it fine at idle

Car is a 91 RS Legacy

I have a parallel fuel setup, front mount, forward facing plenum, gizzmo chipped ecu (also have the factory one which made no difference)

other test i did do - not sure if this is the correct way to do it

but while the engine was running i put 10psi via an a/c compressor to see if the fuel pressure would increase on the regulator and it jumped straight up...

Any suggestions would be great as i\'m kinda going bonkers over this one - happy to send beer anywhere in the country!

[lachlan]

is your boost line for the reg plumbed to the intake manifold ? so it gets vac and boost ? / not conneted to the ic pipes or anything

/ if you pull the vac line off while its running does it suck air into the intake manifold ? eg the nipple is blocked ?

but you said you put a boost gauge in it . something doesnt add up here

what is the parrallel setup like ? am rails and some t pieces ?

or has someone made it from 2 stock rails ? you dont still have a stock regulator in the system somewhere do you ?

[NTICEN]

Boost line comes direct from the inlet manifold and nothing else is coming off it

if i disconnect the line it sucks air in

Factory rails (two left hand ones i think?) with t pieces in there. I\'m considering just finding a factory setup and putting it all back on there...

def no other reg in there

Strange thing is the car was running fine at the start of the year...

[lachlan]

does fuel pressure drop when the car is idling ? like it should

is it something dumb like the piece of vacuum line your using is blocked ?

[Guest]

Silly and very likely not it but is it missing the oring that seals the vac port on the reg?

Is the reg the right way around?

[NTICEN]

Fuel pressure sits around 37/38psi at idle then 43psi with vac line disconnected

i replaced the vac line as well and still no difference

Doesn\'t appear to have any leaks coming from the regulator - brought the reg brand new from redline on wednesday as i thought my cheap copied verison was to blame

[Eight_dollar]

if pump which you say can be wound up on the reg to 60psi

the only cause can be the reg and hoses or vac/boost supply to it

[Guest]

Have you got the reg the right way round? The input/output fpr the fuel?

[NTICEN]

 Eight dollar said:

if pump which you say can be wound up on the reg to 60psi

the only cause can be the reg and hoses or vac/boost supply to it

Where it makes sense that if the reg isn\'t getting boost pressure it won\'t work but when i T a boost gauge into that line everything looks normal...

Reg a brand new from Redline as i had a cheap one on it before which i thought may be the issue

[NTICEN]

 evowrx said:

Have you got the reg the right way round? The input/output fpr the fuel?

trippled checked that one - 99.9% sure its right unless someones playing tricks on me...

[Guest]

Pic of how its set up? Im sure theyre all the same tho.

[NTICEN]

 evowrx said:

Pic of how its set up? Im sure theyre all the same tho.

will have to post some up tomorrow - left car at workshop

[titian]

Pressure drop loss due to injectors fuelling for boost requrement.

Injector fuel feed lines too small for the system.

This will give indication of no increase in pressure when measured on the return line prior to the fpr under boost.

Replace fuel lines from the tank to the reg with 10mm or 8mm ID as a minimum. Fixed!

[rex-leggy]

ae? dont replace the factory lines .

if they can support 300+ kw they will work on a standard wrx.

post a pic up of how the bits are hooked up and how fuel lines are hooked up.

do you have the reg on the return to the tank? are you certain that the fuel lines are around the correct way?

[funkytown]

mine did this - it would pressurise and return to 0 because i had the feed and return the wrong way round on external pump.

+1 to josh\'s \'EEH WTF"..

[NTICEN]

 rex-leggy said:

ae? dont replace the factory lines .

if they can support 300+ kw they will work on a standard wrx.

post a pic up of how the bits are hooked up and how fuel lines are hooked up.

do you have the reg on the return to the tank? are you certain that the fuel lines are around the correct way?

I double checked the fuel lines - pulled the one off the pump (middle one) and fuel came shooting out

Reconnected then pulled the line off the fuel filter - fuel came out

btw - fuel pressure reg is only sitting there as i brought a brand new one and haven\'t mounted it yet where my old one sat...

[Guest]

Im sure you have the lines round the wrong way. The line to the bottom of reg should be moved to fuel filter input and vice versa.

[lachlan]

That sentance is a bit confusing evo , the reg is never connected to the filter at all

The fuel lines took correct according to every diagram I\'ve seen

[Marky]

 evowrx said:

Im sure you have the lines round the wrong way. The line to the bottom of reg should be moved to fuel filter input and vice versa.

It goes tank --> pump --> filter --> rail --> reg inlet is the side port, reg outlet is the bottom port --> then return to tank. That photo is hooked up right

I\'m scratching my head on whats not working here, if it works to adjust base I cant understand how it\'s not raising with boost

Good Ruck

[loner]

So does the car run okay off boost? how about on boost? I\'d be tempted to test in another way... i.e. test the A/F and exhaust temp when on boost.

Can you post pics of the rest of the setup?

One difference in that pic to my 98 STi, is the order of your fuel lines. On mine:-

bottom = feed

middle = vent

top = return

that\'s probably a difference in the setup, not that you have it wrong.

[Guest]

Yep that was confusing all right. I just think those lines are the wrong way round like the feed from tank/pump is confused with return hose to tank if you get what I mean but of course physically looking at it everythings in the right place.

Its acting like the reg is the wrong way round. The actual reg ports etc are all in the same place so can only see the system working backwards.

Just try swapping the lines I said see if it works.

[NTICEN]

 loner said:

So does the car run okay off boost? how about on boost? I\'d be tempted to test in another way... i.e. test the A/F and exhaust temp when on boost.

Can you post pics of the rest of the setup?

One difference in that pic to my 98 STi, is the order of your fuel lines. On mine:-

bottom = feed

middle = vent

top = return

that\'s probably a difference in the setup, not that you have it wrong.

If running 10psi or lower the car seems to run fine - Off boost the car is perfect as far as I know

I\'ll see if I can get the a/f and exhaust temp tested and will go take another pic of the engine bay soon

I\'ve got a V1 WRX right next to at work today so will just compare to this car also

[NTICEN]

 evowrx said:

Yep that was confusing all right. I just think those lines are the wrong way round like the feed from tank/pump is confused with return hose to tank if you get what I mean but of course physically looking at it everythings in the right place.

Its acting like the reg is the wrong way round. The actual reg ports etc are all in the same place so can only see the system working backwards.

Just try swapping the lines I said see if it works.

I\'ve got no issue swapping the lines over to see if it will work - But after last nights test, am I right that the middle line off the fuel pump assy if the feed line?

and also btw - thanks for everyones input so far!

[NTICEN]

[D-Style]

Looks like you have Reg pipes wrong way round.